1. Field of the Invention
The present invention relates to a driver IC packaging module and a flat display device using the same.
2. Description of the Prior Art
The progress in development of the display device using the flat display panel has been notable, in recent years. In particular, since the AC PDP (Plasma Display Panel) device with the triple-electrode surface discharge structure can easily fabricated as the large-area color display panel, practical implementation and application of the AC PDP make progress in the field of the large size television, etc.
FIG. 1 is a schematic plan view showing the AC PDP device with the triple-electrode surface discharge structure and a block diagram showing a driver circuit therein. FIG. 2 is a sectional view showing display cells in the AC PDP device.
In the AC PDP panel, a front glass substrate 101 and a rear glass substrate 102 are arranged at a distance to oppose to each other.
A plurality of display sustaining electrodes made of transparent conductive material are formed in parallel on an opposing surface of the front glass substrate 101 opposing to the rear glass substrate 102. The sustaining electrodes consist of X electrodes xn (n is an integer) and Y electrodes yn (n is an integer), which are arranged alternatively. The sustaining voltage is applied to the X electrode xn and the Y electrode yn which partition one luminous displayed cell area 103.
Also, a plurality of address electrodes am (m is integer) are arranged on an opposing surface of the rear glass substrate 102 opposing to the front glass substrate 101 so as to intersect orthogonally with the sustaining electrodes xn, yn. A space in which one address electrode am is intersected with a set of sustaining electrodes xn, yn constitutes a single display cell 103. Depending upon whether or not the address voltage is applied selectively to these address electrodes am, either display or non-display of the display cell 103 can be selected.
The sustaining electrodes xn, yn are covered with a protection film 104, and the address electrodes am is covered with a dielectric film 105. Insulating partitions 106 are formed on respective areas of the dielectric film 105 on both sides of the address electrodes am. Red, green, or blue fluorescent material 107 is coated on a surface of the dielectric film 105 between the partitions 106.
In this case, an inter-opposing electrode capacitance Cg is present between the address electrode am and the sustaining electrodes xn, yn, and an inter-neighboring electrode capacitance Ca is present between the address electrodes am.
As shown in FIG. 1, principal portions of the AC PDP driver circuit comprises an address driver circuit 111 for driving the address electrodes am, a scanning driver circuit 112 for driving and scanning the Y electrodes yn independently, a Y common driver circuit 113 for applying the sustaining voltage to the Y electrodes yn via the scanning driver circuit 112, an X common driver circuit 114 for applying the sustaining voltage to the X electrodes xn and, a controller circuit 115 for controlling these driver circuits 111 to 114.
The controller circuit 115 comprises a display data controller 116 for driving the address driver circuit 111 based on a clock signal CLK an d display data D supplied from external devices, a scanning driver controller 117 for driving the scanning driver circuit 112 in accordance with the horizontal synchronizing signal Hsync and the vertical synchronizing signal Vsync supplied from external devices and, a common driver controller 118 for driving the X common driver circuit 114 and the Y common driver circuit 113 in accordance with the horizontal synchronizing signal Hsync and the vertical synchronizing signal Vsync being input from external devices. The display data controller 116 has a frame memory 119 for storing display data.
In the above circuit configuration, the scanning driver circuit 112 and the address driver circuit 111 need circuits which apply selectively a driving pulse to a plurality of Y electrodes yn and a plurality of address electrodes am. Normally, IC semiconductor devices are employed as principal circuit parts in such circuits.
For example, in the 42-inch PDP device, 480 Y electrodes yn are provided on the scanning side, and 2556 (852 pixelxc3x973 (RGB)) address electrodes am are provided on the address side. Thus, the drivers (driving circuits) which have output pads connected to these electrodes on a one-by-one correspondence are required.
Normally, a driver IC chip in which 64 driver elements for driving 64 electrodes are integrated is employed as such drivers.
Therefore, in most cases, 8 driver ICs are prepared for the 480 Y electrodes on the Y electrode side, and 40 driver ICs are prepared for the 2556 address electrodes on the address electrode side.
In order to incorporate a number of driver ICs into the PDP device as the driver circuits, the high density packaging technology which can provide electrical connection to a number of electrodes without fail with high reliability and can mount these small and thin driver circuits on the rear side of the display panel is requested.
For example, as shown in FIG. 3, the conventional PDP device has such a structure that a display panel 123 is stuck on one surface of a chassis 122 which is constructed by intersecting a plurality of beam members 120, 121 mutually and a plurality of driver IC chips are mounted on the other surface of the chassis 122. Each of the beam members 120, 121 is formed as a metal rod body which has a sectional shape like a hat.
As the driver IC chip packaging structure, an approach of integrating a plurality of driver IC chips on one substrate as a module and then incorporating this module into the PDP device is adopted. As such driver IC packaging module, there are the COB (Chip On Board) structure shown in FIGS. 4A and 4B or the COM (Chip On Multiple Board) structure shown in FIGS. 5A and 5B.
As shown in FIGS. 4A and 4B, the COB structure comprises a printed substrate 131, a flexible flat cable (abbreviated simply as xe2x80x9cFFCxe2x80x9d hereinafter) 132 which is thermocompression-bonded to one side portion of the printed substrate 131, and a flexible substrate 133 which is thermocompression-bonded to the other side portion of the printed substrate 131. Also, the COB structure has such a structure that a plurality of bare-chip driver ICs 130 are directly mounted on the printed substrate 131 and various pads (not shown) on the driver ICs 130 are connected to wirings 134, 135 on the printed substrate 131 via the wire bonding. As the pads on the driver ICs 130, there are power supply pads, input signal pads, output pads, etc.
A plurality of wirings 135 on the output side on the printed substrate 131 are connected to a plurality of wirings 136 on the flexible substrate 133 one by one by the thermocompression bonding respectively. Also, a plurality of wirings 134 on the input side on the printed substrate 131 are connected to a plurality of wirings 137 on the FFC 132 one by one by the solder respectively.
In FIG. 4B, a reference 138a denotes input signal and power supply wiring patterns of formed on a back surface of the printed substrate 131 on the input side. The wiring patterns 138a have a three-dimensional wiring structure which can distribute various wirings being input from the FFC 132 to a plurality of driver ICs 130 by utilizing through-holes or wiring patterns on the back surface of the substrate. In FIG. 4B, a reference 138b denotes a high voltage power supply pattern formed on the back surface on the output side, 138c denotes an earth pattern formed below the driver ICs 130 on the back surface, and 139 denotes a voltage power supply pattern formed on an upper surface of the printed substrate 131.
On the contrary, as shown in FIGS. 5A and 5B, the COM structure comprises a printed substrate 141, an FFC 142 which is adhered to one side portion of the printed substrate 141 by the solder, and a flexible substrate 143 which is adhered to the other side portion of the printed substrate 141. A plurality of pads on the bare chip driver ICs 140 on the output side are connected to a plurality of wirings 146 on the flexible substrate 143 one by one via the wire bonding. The input signal and power supply wiring patterns 145 on the printed substrate 141 have a three-dimensional wiring structure which can distribute various wirings being input from the FFC 142 to a plurality of driver ICs 140 by utilizing through-holes in the substrate or wiring patterns on the back surface of the substrate. One ends of these wirings 145 are connected one by one to input signal and power supply pads of respective driver ICs 140 by the wire bonding.
In FIG. 5B, a reference 148a denotes input signal an power supply wiring patterns formed on the back surface of the printed substrate 141 on the input side, 148b denotes an earth pattern formed on the back surface below the driver ICs 140, and 148c denotes high voltage power supply patterns formed on the output side of the surface of the printed substrate 141.
According to the driver IC packaging module having the COM structure, since the connection of wirings on the output side of the driver ICs via the thermocompression bonding is not needed, the COM structure can achieve the higher reliability and the higher density than the COB structure.
As described above, because of difference in the packaging configuration between the COB structure and the COM structure, the output sides of the wirings on the flexible substrates 134, 144 are exposed in the opposite direction to the upper surfaces of the printed substrates 131, 141 (fitting surfaces of the driver ICs 130, 140) in the COB structure and the COM structure.
In other words, the mounting surface of the driver ICs 130 and the exposed surface of output ends of the wirings 136 on the flexible substrate are directed in the opposite direction to each other in the COB structure, whereas the mounting surface of the driver ICs 140 and the exposed surface of output ends of the wirings 146 on the flexible substrate 143 are directed in the same direction in the COM structure.
Next, fitting of the driver IC packaging module onto a chassis 122 of the surface discharge AC PDP device will be explained hereunder.
The driver IC packaging module Ml having the COB structure shown in FIGS. 4A and 4B are secured onto the beam elements 121 of the chassis 122 by driving screws 127 via an insulating sheet 126 and the printed substrate 131 into the beam elements 121, as shown in FIG. 6, for example. In this case, since the IC chip mounting surface of the printed substrate 131 and the output terminal surfaces on the flexible substrate 133 are present oppositely, the module M1 can be fitted to be secured such that the back side of the IC chip mounting surface is directed to the panel 123. Here the printed substrate 131 may be fixed to the chassis 122 by the screws while using cylindrical bosses in place of the insulating sheet 126.
In contrast, the driver IC packaging module M2 having the COM structure shown in FIG. 5 can be fitted to secure the printed substrate 141 to top surfaces of the cylindrical bosses 124, which are fitted onto the beam member 121 of the chassis 122, as shown in FIG. 7, for example, by using screws 125. In this case, since the IC chip mounting surface of the printed substrate 141 and the exposed surfaces of the wirings 146 on the flexible substrate 143 are directed to the same direction, the IC chip mounting surface of the printed substrate 141 can be secured to direct to the panel 123.
Next, the overall circuit of the driver IC packaging module employed in the address driver circuit 111 shown in FIG. 1 will be explained simply hereunder.
As shown in FIG. 8A, the driver IC packaging module has a plurality of driver ICs 130, 140 described above, and then a high voltage power supply line VH, a low voltage power supply line VL, a signal line SG, and a ground voltage line GND are connected to respective input pads of the driver ICs 130, 140.
A high voltage bypass capacitor CH is connected between the high voltage power supply line VH and the ground voltage line GND, and a low voltage bypass capacitor CH is connected between the low voltage power supply line VL and the ground voltage line GND. The high voltage power supply line VH, the low voltage power supply line VL, the signal line SG, and the ground voltage line GND are input from wirings of the flexible flat cable (FFC), then divided into plural lines via input wirings on the substrate side, and then input into the driver ICs 130, 140 in parallel.
The signal line SG has a plurality of wirings to transmit a clock signal CLK, data D, a latch signal LATCH, and a strobe signal STB.
As shown in FIG. 8B, for example, the driver ICs 130, 140 has such a structure that a 64-bit shift register SR, a 64-bit latch L, and a 64-bit gate G are connected in series. A data signal D and a clock signal CLK are input into the 64-bit shift register SR via a signal line, and also a low voltage is applied to the 64-bit shift register SR from the low voltage power supply line VL. Also, the latch signal LACH is input into the 64-bit latch L, and the strobe signal STB is input into the 64-bit gate G. Further, the ground voltage line GND is connected to the 64-bit shift register SR, the 64-bit latch L, and the 64-bit gate G respectively.
Meanwhile, output buffers BF1 to BF64 are connected to 64 output terminals of the 64-bit gate G individually. The high voltage power supply line VH and the ground voltage line GND are connected to power supply ends of these connection buffers BF1 to BF64 to supply a high voltage. A low voltage signal is input into signal input ends of the connection buffers BF1 to BF64 such that a high voltage signal is output from their output ends in response to the signal. The signal output from the output ends is sent to the address electrodes am.
In this event, in order to assure a stable operation of the driver IC packaging module shown in FIGS. 4A, 4B and 5A, 5B for a long term, a structure for suppressing heat generation of the driver IC is needed.
More particularly, in the emissive display panel such as the AC PDP device, the EL display device, etc., not only the supply of the luminescence energy to pixels but also the supply of the charge and discharge current to capacitor components of the panel is needed based on the principle operation characteristic. Therefore, there is such a tendency that the current flowing through the inside of the driver IC is increased to enhance an amount of heat generation in the driver IC itself and thus power loss in the inside is increased up to an unnegligible level.
Especially, in the 42-inch large size panel, since the number of pixels per electrode of the display panel is large, the power consumption in each driver IC is increased to enhance an amount of heat generation more and more. Hence, an appropriate configuration which can radiate effectively the generated heat to the outside to suppress the temperature rise of the driver IC per se is indispensable for the panel.
However, in the driver IC packaging module having the COM structure shown in FIGS. 5A, 5B and 7 and the fitting structure in the prior art, the heat generated in the driver IC 130 has no escape except the printed substrate 131 and thus such heat is kept between the printed substrate 131 and the frame 122. Therefore, there is a possibility that, since the temperature of the driver IC 130 itself is increased, the long-term reliability cannot be assured.
On the contrary, in the driver IC packaging module having the COB structure shown in FIGS. 4A, 4B and 6 and the fitting structure in the prior art, a part of the chassis 122 is utilized as a radiation board. It is preferable that the heat should be radiated from the driver IC 130 by providing a convex tool to the chassis 122 or bringing the back surface of the printed substrate 131 into contact to the chassis 122 directly.
However, in the driver IC packaging module having the COB structure in the prior art, since the high voltage power supply wiring and the signal line are formed on the back surface side of the printed substrate 131, it is impossible to bring the back surface of the printed substrate 131 into contact to the tool or the chassis directly and thus the insulating sheet 126 cannot be omitted.
As a result, the heat radiation from the printed substrate 131 to the chassis 122 is carried out via the insulating sheet 126. Therefore, it is the existing state that the heat radiation effect has the limit and does not come up to a level which can assure the reliability.
Further, as described above, the configuration for connecting the output side wirings on the printed substrate 131 and the wirings on the flexible substrate 133 mutually by the thermocompression bonding is indispensable for the COB structure. However, since pitches of the wirings which are arranged in great numbers on the printed substrate 131 and the flexible substrate 133 are fine, short-circuit occurs between the wirings when alignment of the opposing wirings is displaced, or defective contact due to mixture of foreign matters occurs easily. In particular, as the wiring pitch become higher definition and the wiring length becomes longer, it becomes difficult to assure the connection quality and the reliability.
It is an object of the present invention to provide a driver IC packaging module which includes an IC module having a high heat radiating effect or a chassis structure having a high heat radiating efficiency, and a flat display device using the same.
According to an aspect of the present invention, in the driver IC packaging module fitted to the flat display device, one end portion, which are connected to the display panel electrodes, of the wirings which are passed through the flexible substrate fitted to an area located in the neighborhood of one end of the driver IC chip mounting surface is exposed in the opposite direction to the driver IC chip mounting surface.
Therefore, it is possible to direct the driver IC chip mounting surface to the rear surface side and connect one end portion of the electrodes of the flexible substrate to electrodes on a front surface of the display panel by bending the flexible substrate. As a result, a structure which brings the back surface (surface opposite to the driver IC chip mounting surface) of the module substrate into contact to the surface of the chassis can be achieved easily, the chassis per se can be ready to be. utilized as the heat radiation plate for the heat generated by the substrate, and thus a structure of the flat display device which can improve the thermal characteristic of the module and can be installed compactly can be achieved.
Also, according to another aspect of the present invention, the mechanical strength can be maintained by attaching the beam-like structure to the chassis on the rear surface of the display panel or forming a part of the chassis itself as the beam-like structure, and also the substrate surface of the driver IC packaging module can come into contact into the flat plate surface of this beam-like structure. Therefore, the heat generated from the driver IC chip can be diffused to the chassis via the beam.
That is, the thermal characteristic can be improved by causing the chassis per se to have the function of radiating the heat generated by the driver IC chip, and also the built-in packaging structure whose thickness is small and whose thermal characteristic can be improved as a whole can be achieved while holding the original mechanical strength of the chassis as it is.
Especially, according to the structure in which the chassis is formed of the flat metal plate having a size to cover substantially the overall rear surface side of the panel, because the chassis is formed to have a wide area, such chassis can have the effect as the heat radiation and thermal diffusion plate for not only the heat generated by the driver IC chip but also the heat generated by the display panel and other driver circuit substrates. Therefore, the thermal characteristic of the overall device can be improved and the mechanical strength can be still maintained by attaching the beam. As a result, the thin flat display device having the sufficient mechanical strength can be achieved.